A conventional light reduction device reduces light, for example, by blocking a light path using diaphragm blades or by absorbing or reflecting the light using a neutral density filter (hereinafter, referred to as “ND filter”).
For example, Patent Literature 1 discloses a light reduction device for adjusting reduction of the light by applying a current to a driving coil to control an aperture of the diaphragm blades, which are biased to be closed, to open against the biasing force.
According to the light reduction device disclosed in Patent Literature 1, a lower diaphragm blade and an upper diaphragm blade which overlap each other are shifted in parallel with each other by force generated by an actuator so as to vary an aperture formed between the blades, thereby blocking a light beam and reducing the light.
A center of the aperture is defined to be coincident with a center of an optical axis of a lens, so that a distance between the two blades is controlled to adjust an amount of the reduced light optimally.
As is also disclosed in Patent Literature 2, another light reduction device has been proposed which uses the diaphragm blade and the ND filter.
According to the light reduction device disclosed in Patent Literature 2, the diaphragm blade is shifted on a plane orthogonal to the optical axis to allow an aperture to be variable, and the ND filter is shifted on the plane orthogonal to the optical axis to cause an amount of transmissive light to be variable. The light-reduction adjustment is thus performed.
The ND filter is previously placed at an area out of an aperture area, and the light reduction device disclosed in Patent Literature 2 shifts the ND filter which has an optimal light-reduction level to cover the aperture area.
Similar to in the light reduction device disclosed in the Patent Literature 1, in the light reduction device disclosed in Patent Literature 2, the center of the aperture is also placed to be coincident with the center of the optical axis of the lens, and the diaphragm blade and the ND filter are placed over the aperture to adjust and reduce the light.
Patent Literature 3 proposes a light reduction device which employs a turret diaphragm plate made of a super thin plate having a sheet shape.
The light reduction device disclosed in Patent Literature 3 includes a curved oscillation plate perforated by a plurality of apertures having mutually different aperture diameters, and selects a proper aperture by repeatedly oscillating the curved oscillation plate laterally at a certain angle.
With this configuration, according to the light reduction device disclosed in Patent Literature 3, the aperture can be easily placed on the optical axis, so that the light amount can be reduced according to a size of the aperture.